: I can think of a simple explanation... Bungie wanted to ensure that you
: always have 6 minutes (or 5, in Legendary) at the start of the Warthog
: run. However, Bungie cannot guarantee that you're going to figure out
: where the access elevator is right away, or even that you're going to head
: there immediately. You might decide to run back to the armory, for
: example. This way, Cortana can still convey the danger of the situation
: ("We have fifteen minutes"), but Bungie won't worry about the
: player making it impossible for themselves to reach the end of the level.
: It does checkpoint when you reach the 'Hog for the first time, you know.
: :-)

BTW, once you crack all the engine shields you can't go back to the Armory to resupply. Your point is still valid however.

One other thing, in The Maw:

343 GUILTY SPARK:

Why do you continue to fight us, Reclaimer? You cannot win! Give us the construct, and I will endeavour to make your death relatively painless and -

(Another tone sounds)

CORTANA:

At least I still have control over the comm channels.

If Cortana has control over the comm channels I guess a possibility exists that she can hide communications and the like from the Master Chief?